Western Washington Phase II Municipal Stormwater Permit
Open comment periods
MS4 Phase I permit modification
Comment period: Aug. 5 through Nov. 2, 2026
Online public hearing: Sept. 9, 2026, 2 p.m.
MS4 Phase I and II permit: Early input for 2029 reissuance
Early input period: July 24, 2026, through Feb. 19, 2027
We develop and administer Clean Water Act National Pollutant Discharge Elimination System (NPDES) municipal stormwater permits in Washington. The Western Washington Phase II permit requires local governments to manage and control stormwater runoff so that it does not pollute downstream waters.
The current permit has been in effect since Aug. 1, 2024, and expires July 31, 2029. We have started the permit reissuance process to identify issues and necessary improvements for the 2029 permits.
Overview of permit timelines
View permit timelines for continuing permittees. These timelines provide an overview of major deadlines for implementing permit requirements.
Annual reports for the calendar year are due by March 31 the following year.
Am I covered by a MS4 permit?
The Phase II permit for Western Washington covers over 80 cities and portions of six counties.
Find a list of cities and counties covered by this permit.
Municipal stormwater permit guidance
For guidance about applying, changing, or implementing and complying with your municipal stormwater permit see municipal stormwater guidance. Stormwater manuals provide stormwater permit implementation and management guidance. For more general stormwater permit guidance, see the stormwater guidance page.
Frequently asked questions
Have a question? Check out our frequently asked questions page.
Permit history
To access previous permits and learn about past permit cycle processes, such as appeals, public comments, and draft reviews, see municipal stormwater history.